Lithographic Apparatus and Device Manufacturing Method

ABSTRACT

A lithographic system includes a monitored lithographic projection apparatus arranged to project a patterned beam onto a substrate. A scatterometer measures a plurality of parameters of the pattern transferred to the substrate including at least one CD-profile parameter and at least one further parameter of the pattern transferred to the substrate which is indicative of a machine setting of the monitored lithographic projection apparatus. A matching system includes a database storing information representative of reference CD values and reference values for the further feature. A comparison arrangement compares the measured values with the corresponding stored values, a lithographic parameter calculation means calculating a corrected set of machine settings for the monitored lithographic apparatus dependent on the differences between the measured and reference values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/707,104, filed Feb. 17, 2010 (now U.S. Pat. No. _,___,___), whichclaims the benefit under 35 U.S.C. §119(e) of U.S. ProvisionalApplication No. 61/155,668, filed Feb. 26, 2009, which are incorporatedby reference herein in their entireties

BACKGROUND

1. Field of the Invention

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device. Embodiments of the invention have particularrelevance to a method and apparatus for adjusting the settings of thelithographic apparatus.

2. Background Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,comprising part of, one, or several dies) on a substrate (e.g., asilicon wafer).Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network ofadjacent target portions that are successively patterned. Knownlithographic apparatus include so-called steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beamin a given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti parallel to this direction. Itis also possible to transfer the pattern from the patterning device tothe substrate by imprinting the pattern onto the substrate.

Where a manufacturing facility has more than one lithographic apparatusused for printing the same product types, it is desirable to be able tomatch the characteristics of all the lithographic apparatus to eachother. This will allow the apparatus to be used in a “mix and match”configuration, in which the apparatus may be arranged to have the sameoptical transfer function.

In one lithographic manufacturing process, a first lithographic transferfunction of a first lithographic projection apparatus is obtained. Theinformation is compared with information relating to a secondlithographic transfer function corresponding to a second lithographicprojection apparatus, which acts as a reference apparatus. Thelithographic transfer function describes the transfer of spatialfrequencies from the pattern on the mask to the pattern projected on thesubstrate. The difference between the first and second information iscalculated. Machine settings for the first lithographic apparatus arechanged in order to minimize the difference so as to improve the matchbetween the first and second lithographic projection apparatus. Theinformation that is obtained on each of the first and second projectionapparatus is critical dimension (CD) pitch anomaly. Variations in CDpitch can occur as a function of variations in the machine settings of alithography apparatus, such as exposure energy and illuminationsettings.

However, there is a problem with this method of matching twolithographic projection apparatus in that the measurement of CD does notallow discrimination of the various lithographic projection apparatusparameters, thus leading to errors.

SUMMARY

It is desirable to provide a method for allowing two lithographicprojection apparatus to be matched, which may be made more accurate thanthe previously known methods.

According to a first embodiment, there is provided a lithographic systemcomprising a monitored lithographic projection apparatus, a metrologyapparatus, and a matching system. The monitored lithographic projectionapparatus is arranged to project a patterned beam of radiation onto asubstrate. The metrology apparatus is arranged to measure valuesrepresentative of a plurality of features of the pattern transferred tothe substrate including values of at least one CD-profile parameter andat least one further feature profile parameter which is indicative of amachine setting of the monitored lithographic projection apparatus. Thematching system comprises a storage system, a comparison system, and alithographic parameter calculation system. The storage system stores areference CD-profile parameter value representative of the CD-profileparameter and a reference feature profile value representative of theone further feature profile parameter. The comparison system comparesthe measured and reference values of the one further feature profileparameter. The lithographic parameter calculation system calculates acorrected set of machine settings for use by the monitored lithographicapparatus dependent on the differences between the measured andreference values of the one further feature profile parameter andbetween the measured and reference values of the CD-profile parameter.

According to a second embodiment, there is provided a matching systemfor use in a lithographic system comprising a monitored lithographicprojection apparatus, a metrology apparatus and the matching system. Themonitored lithographic projection apparatus is arranged to project apatterned beam of radiation onto a substrate. The metrology apparatus isarranged to measure values representative of a plurality of features ofthe pattern transferred to the substrate including at least oneCD-profile parameter and at least one further feature profile parameterwhich is indicative of a machine setting of the monitored lithographicprojection apparatus. The matching system comprises a storage system, acomparison system, and a lithographic parameter system. The storagesystem stores a reference CD-profile parameter value representative ofthe CD-profile parameter and a reference feature profile valuerepresentative of the one further feature profile parameter. Thecomparison system compares the measured and reference values of the onefurther feature profile parameter. The lithographic parametercalculation system calculates a corrected set of machine settings foruse by the monitored lithographic apparatus dependent on the differencesbetween the measured and reference values of the one further featureprofile parameter and between the measured and reference values of theCD-profile parameter.

According to a third embodiment, there is provided a devicemanufacturing method comprising the following steps. Projecting apatterned beam of radiation onto a substrate. Measuring valuesrepresentative of a plurality of features of the pattern transferred tothe substrate including values of at least one CD-profile parameter andat least one further feature profile parameter which is indicative of amachine setting of a monitored lithographic projection apparatus.Storing a reference CD-profile parameter value and a reference featureprofile value representative of the one further feature profileparameter. Comparing the measured and reference values of the onefurther feature profile parameter. Calculating a corrected set ofmachine settings for use by the monitored lithographic apparatusdependent on the differences between the measured and reference valuesof the one further feature profile parameter and between the measuredand reference values of the CD-profile parameter. Correcting the valuesof the machine settings according to the corrected set of machinesettings.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention

FIG. 1 depicts a lithographic projection apparatus, according to anembodiment of the invention.

FIG. 2 is a flow diagram depicts the apparatus of FIG. 1 incorporated ina system which may be used in a method in accordance with an embodimentof the invention allowing the characteristics of the apparatus to bematched to those of a reference lithographic projection apparatus.

FIG. 3 illustrates a method of matching a lithographic projectionapparatus to a reference lithographic projection apparatus using thesystem shown in FIG. 2, according to an embodiment of the presentinvention.

FIG. 4 depicts the sensitivity of a one dimensional target to sigmacenter variations for various focus states of the lithographic processcarried out in the apparatus in FIG. 1, according to an embodiment ofthe present invention.

FIG. 5 illustrates a variation of side wall angle (SWA) as a function ofthe focus setting, according to an embodiment of the present invention.

FIG. 6 illustrates the difference in mid critical dimension (mid-CD) asa function of the dose, according to an embodiment of the presentinvention.

FIG. 7 depicts a method of matching two scanners, according to anembodiment of the present invention.

FIG. 8 depicts a method of matching two scanners, according to anembodiment of the present invention.

FIG. 9 illustrates a further lithography system which may be used in amethod, according to an embodiment of the present invention.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

This specification discloses one or more embodiments that incorporatethe features of this invention. The disclosed embodiment(s) merelyexemplify the invention. The scope of the invention is not limited tothe disclosed embodiment(s). The invention is defined by the claimsappended hereto.

The embodiment(s) described, and references in the specification to “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment(s) described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to effect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other forms of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.), and others. Further,firmware, software, routines, instructions may be described herein asperforming certain actions. However, it should be appreciated that suchdescriptions are merely for convenience and that such actions in factresult from computing devices, processors, controllers, or other devicesexecuting the firmware, software, routines, instructions, etc.

Before describing such embodiments in more detail, however, it isinstructive to present an example environment in which embodiments ofthe present invention may be implemented.

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises an illuminationsystem (illuminator) IL configured to condition a radiation beam B(e.g., UV radiation or DUV radiation); a support structure (e.g., a masktable) MT constructed to support a patterning device (e.g., a mask) MAand connected to a first positioner PM configured to accurately positionthe patterning device in accordance with certain parameters; a substratetable (e.g., a wafer table) WT constructed to hold a substrate (e.g., aresist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters; and a projection system (e.g., a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g., comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e., bears the weight of, thepatterning device. It holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.,employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g., employing a programmable mirror array of a typeas referred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g., water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g., an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g., so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam B, e.g., after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

-   -   1. In step mode, the mask table MT and the substrate table WT        are kept essentially stationary, while an entire pattern        imparted to the radiation beam is projected onto a target        portion C at one time (i.e., a single static exposure). The        substrate table WT is then shifted in the X and/or Y direction        so that a different target portion C can be exposed. In step        mode, the maximum size of the exposure field limits the size of        the target portion C imaged in a single static exposure.    -   2. In scan mode, the mask table MT and the substrate table WT        are scanned synchronously while a pattern imparted to the        radiation beam is projected onto a target portion C (i.e., a        single dynamic exposure). The velocity and direction of the        substrate table WT relative to the mask table MT may be        determined by the (de-) magnification and image reversal        characteristics of the projection system PS. In scan mode, the        maximum size of the exposure field limits the width (in the        non-scanning direction) of the target portion in a single        dynamic exposure, whereas the length of the scanning motion        determines the height (in the scanning direction) of the target        portion.    -   3. In another mode, the mask table MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the radiation beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 is a flow diagram depicts the apparatus of FIG. 1 incorporated ina system which may be used in a method in accordance with an embodimentof the invention allowing the characteristics of the apparatus to bematched to those of a reference lithographic projection apparatus. Inorder to match the characteristics of the lithography apparatus with areference lithography apparatus a matching system may be used. Thematching system matches the characteristics of test wafers produced bythe lithography apparatus with the wafers produced by a referencelithography apparatus. The matching allows adjustments to be made to thelithography apparatus in order to match the lithographic transferfunctions of the two lithography apparatus. In the particular system tobe described by way of example, the lithography apparatus is a scanner,although it will be appreciated that the embodiments of the invention isapplicable to other types of lithography apparatus, for examplesteppers.

A lithography system discussing in general transfer functions can befound in U.S. Pat. No. 6,795,163, which is incorporated herein byreference in its entirety.

In the example shown in FIG. 2, a scanner 21 to be matched is responsiveto instructions from a manufacturing execution system 22. Wafersproduced by the scanner 21 are measured by a metrology tool in the formof a scatterometer 23. Profile information from the scatterometer is fedto a lithographic apparatus matching system indicated generally as 24.The lithographic apparatus matching system 24 includes a data storagesystem 25, a scanner tuning system 26, and a user interface 27.

FIG. 3 illustrates the process steps carried out by the system shown inFIG. 2, according to one embodiment of the present invention. In stepS31, wafers are exposed according to a manufacturer's recipe provided tothe scanner 21 by the manufacturing executing system 22 and CD-profileparameter values of the wafers are measured using the scatterometer 23in step S32. In step S33, the measured values of the CD-profileparameters are compared with values of the parameters for the referencescanner, which are stored in the customer file system 25. The scannertuning server 26 derives correction values to change the recipe forexposing the wafers applied by the scanner 21 in step S34. The wafersare then re-measured, to determine if the scanner being set upsufficiently matches the lithography the reference scanner, eitherautomatically or using user intervention via user instructions input viathe user interface 27. For example, this can be done by comparing thelithography transfer functions of the two scanners or by other methodssuch as by comparing the proximity (delta) curves, which are a plot ofCD-profile parameter values as a function of pitch, i.e., the inverse ofthe spatial frequency, for the two scanners.

FIG. 4 depicts the sensitivity of a one dimensional target to sigmacenter variations for various focus states of the lithographic processcarried out in the apparatus in FIG. 1, according to an embodiment ofthe present invention. In one example, measurement of CD-profileparameter value alone does not allow for scanner parameters and processparameters to be discriminated so as to allow a scanner to be accuratelymatched with the parameters of a reference scanner. In one example, asensitivity of a one-dimensional target to variations in sigma-center,that is (σ-outer+σ-inner)/2. In this example, the sensitivity is shownfor various focus states of the lithography process. It can be seen thatas the defocus increases, there is an increase in sensitivity tosigma-center. It can be shown that other features of the pattern on thewafer can be correlated with values of the machine settings.

In accordance with an embodiment of the present invention, in additionto the CD-profile parameter value measurements, values representative ofone or more process or scanner related parameters which may be derivedfrom features of the pattern formed on the wafer, are also measured andmatched against the corresponding stored values obtained from areference scanner or against stored values obtained from an earlier runof the monitored scanner. In this example, it is possible to takeaccount of the sensitivity of feature profile parameters of the patternto process related parameters, such as the focus state, or dose state ofthe lithography process or lithography apparatus related parameters,such as numerical aperture (NA) and sigma.

In accordance with an embodiment of the present invention, in additionto measurement of the CD-parameter values by the metrology tool 23,parameters of the exposed resist on the wafer can be measured. Forexample, side wall angle (SWA), resist height and the underlying layerthicknesses (dependent on the stack being measured), such as oxide layerthicknesses, nitride layer thicknesses and BARC thicknesses, togetherwith optical constants such as n and k, are compared to correspondingvalues for the reference scanner.

FIG. 5 illustrates a variation of side wall angle (SWA) as a function ofthe focus setting, according to an embodiment of the present invention.In one example, there is a correlation between side wall angle (SWA) offeatures formed by the resist and focus setting. Thus, it is possible touse SWA information to determine the focus state of the lithoclustercomprising the lithography apparatus and the track, in particular acombination of the scanner focal plane in combination with the usedresist processing stability. As a variation in resist processing canlead to a difference in lithographic transfer function. This may bedetected from the profile information given by the measured features.For example, the relationship between the remaining resist of aparticular feature and the scanner defocus may vary compared to that fora feature of a different pitch. Thus, a change in the processingparameters can be monitored and possibly be compensated for.

FIG. 6 illustrates the difference in mid critical dimension (mid-CD) asa function of the dose, according to an embodiment of the presentinvention. In one example, the mid-CD profile parameter, that is themeasured CD at half height of the resist feature assuming thereconstructed line profile is a simple trapezium, can be used todetermine the dose state of the lithocluster. It will be appreciatedthat, while FIG. 6 illustrates the influence of the value of the mid-CDparameter on the dose, values of other parameters like the bottom CD, ortop CD or any other CD value may be measured. Furthermore more complexprofiles, other than a simple trapezium are possible.

FIG. 7 depicts a method of matching two scanners, according to anembodiment of the present invention. In one example, dedicated focusand/or dose targets on a wafer may be used to separate out the focusand/or dose from the other scanner related parameters. Thus, in stepS71, the dedicated focus and/or dose targets on a wafer, or possiblyseparate wafers, are exposed by the monitored scanner 21 and the SWAand/or mid-CD measured by a scatterometer in step S72. The values arecompared with stored values of the SWA and/or mid-CD, which have beenpreviously measured for a reference scanner in step S73. The acquiredprofile information may be used to allow dedicated focus adjustment ofthe monitored scanner in step S74 either by a mathematically modeledcorrection using the previously measured SWA-focus characteristic of thereference scanner or by physically adjusting the monitored scanner andexposing one or more further test wafers. Additionally, oralternatively, a procedure may be performed for the mid-CD/dosemeasurements.

It will be appreciated that alternatively or additionally to monitoringfocus and dose as described above, dedicated process monitor targets,such as numerical aperture NA and sigma gauges, can be used to separatescanner related parameters such as NA and sigma from general processrelated parameters such as resist processing variations such as coatthickness variations, post exposure bake (PEB) delays and PEBnonuniformities. Furthermore, using different reticle biased targetshaving the same pitch but with the CD/pitch ratio varied, will allow thedifferent parts of the lithography transfer function to bedistinguished. Since the pitch is the same, the light traveling throughthe scanner follows the same optical path. The effect of the processingon the resist and the sensitivity of the various scanner parameters,such as NA, sigma, focus etc. depends also on the CD/pitch ratio,measurement of the CD/pitch ratio thus yielding further information.

FIG. 8 depicts a method of matching two scanners, according to anembodiment of the present invention. In one example, optimization of themachine settings of the monitored scanner may be performed in severalways. In the particular example shown in FIG. 8, at least one dedicatedfocus scatterometer target on a wafer is exposed in step S81 and the SWAmeasured to extract the relevant focus information in step S82 asdescribed above. The focus of the scanner is then corrected in step S83and a second wafer exposed and used to derive other parameter values, inparticular CD.

Alternatively the various parameters may be measured as set out above.All the parameters including the SWA sensitivity of all the variablemachine settings may be put into an optimization program using themeasured and reference profile values leading to an optimized machinesetting.

It will be appreciated that while scanner matching is generallyperformed once at setup, with scanner stability being assumed, scannermatching may be performed periodically or in response to a scannermaintenance or upgrade action. There is a possibility that scannerparameters such as NA, sigma may drift with time, as may the lithographyprocess in general. This will show up as a variation of the lithographictransfer function with time, as well as other measurements such as theproximity (delta) curve. A method in accordance with an embodiment ofthe invention may be used to monitor a scanner for any such variationsand to make corrections during the use of the scanner. Thus, thecharacteristics of the scanner may be compared with its own previouscharacteristics, rather than those of a different reference scanner.

FIG. 9 illustrates a further lithography system which may be used in amethod, according to an embodiment of the present invention. In oneexample, the lithography system may be used in such a mode, equivalentfeatures to those depicted in FIG. 2 being correspondingly labeled. Inone example, a control loop is set up using the output of thescanner-tuning server to provide an input to the manufacturing executionsystem 22. Repetitive measurements of one or more particular featuresmay be made, for example of focus using measurements of, for example,the SWA of a test pattern on the wafers exposed by the scanner 21. Thestability and/or the validity of the scanner 21 can thus be monitored,if required automatically.

It will be appreciated that by measurement of the profile parameter(s)in addition to the measurement of the CD, the matching of twolithographic apparatus may be made more accurate as there is a betterdetermination of the scanner sensitivities. The “to-be-matched”lithographic apparatus may be better directed to the required matchingset point as a better discrimination between various scanner parameterscan be made.

It will also be appreciated that many of the machine settings can bematched by monitoring of appropriate features on the pattern transferredto the wafer. Such machine settings include the ellipticity of theprojection beam, laser bandwidth, focus drilling and oscillationsapplied to the wafer table.

It will also be appreciated that while in the embodiments of theinvention described above, a scatterometer is used as the metrologytool, other metrology tools may be used, for example an SEM measurementtool or an atomic force microscope. A scatterometer however typicallyhas got a shorter measurement time allowing the matching performance tobe made faster.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithographytopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g., having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g., semiconductor memory, magnetic or optical disk) havingsuch a computer program stored therein.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, the Examiner is also reminded that anydisclaimer made in the instant application should not be read into oragainst the parent application.

1. A lithographic system, comprising: a monitored lithographicprojection apparatus arranged to project a patterned beam of radiationonto a substrate; a metrology apparatus arranged to measure valuesrepresentative of a plurality of features of a pattern transferred ontothe substrate including values of at least one CD-profile parameter andat least one further feature profile parameter which is indicative of amachine setting of the monitored lithographic projection apparatus; anda matching system comprising, a storage system configured to store areference CD-profile parameter value representative of the CD-profileparameter and a reference feature profile value representative of theone further feature profile parameter, a comparison system configured tocompare the measured and reference values of the one further featureprofile parameter, and a lithographic parameter determination systemconfigured to determine a corrected set of machine settings for use bythe monitored lithographic apparatus dependent on the differencesbetween the measured and reference values of the one further featureprofile parameter and between the measured and reference values of theCD-profile parameter.
 2. The system according to claim 1, wherein themachine settings comprise focus setting of the test substrate, exposuredose, illumination setting, or numerical aperture.
 3. The systemaccording to claim 2, wherein the feature profile parameter is side wallangle and the machine setting is focus.
 4. The system according to claim2, further comprising a correlating system configured to correlate anarrangement for correlating the CD measurements to the exposure dose. 5.The system according to claim 1, wherein the test substrate includes atleast one dedicated parameter sensitive target effective to allow ameasurement to be made of the one further feature profile parameterdistinct from other feature profile parameters.
 6. The system accordingto claim 1, wherein the reference CD values and the reference values ofthe one further feature profile parameters are based on measurements ofa substrate on which a pattern has been produced by a referencelithographic projection apparatus.
 7. The system according to claim 1,wherein the reference CD values and the reference values of the onefurther feature profile parameter are based on measurements of asubstrate on which a pattern has previously been produced by themonitored lithographic projection apparatus.
 8. A matching systemcomprising: a storage system configured to store measured and referenceCD-profile parameter values representative of a CD-profile parameter andmeasured and reference feature profile values representative of onefurther feature profile parameter which is indicative of a machinesetting of a monitored lithographic projection apparatus; a comparatorconfigured to compare measured and reference values of the one furtherfeature profile parameter; and a lithographic parameter determiningdevice configured to determine a corrected set of machine settings foruse by the monitored lithographic apparatus dependent on the differencesbetween the measured and reference values of the one further featureprofile parameter and between the measured and reference values of theCD-profile parameter.
 9. The system according to claim 8, wherein themachine settings comprise focus setting of the test substrate, exposuredose, illumination setting, or numerical aperture.
 10. The systemaccording to claim 9, wherein the feature profile parameter is side wallangle and the machine setting is focus.
 11. The system according toclaim 9, further comprising a correlating system configured to correlatean arrangement for correlating the CD measurements to the exposure dose.12. The system according to claim 8, wherein the test substrate includesat least one dedicated parameter sensitive target effective to allow ameasurement to be made of the one further feature profile parameterdistinct from other feature profile parameters.
 13. The system accordingto claim 8, wherein the reference CD values and the reference values ofthe one further feature profile parameters are based on measurements ofa substrate on which a pattern has been produced by a referencelithographic projection apparatus.
 14. The system according to claim 8,wherein the reference CD values and the reference values of the onefurther feature profile parameter are based on measurements of asubstrate on which a pattern has previously been produced by themonitored lithographic projection apparatus.